thirst

thirst, sensation indicating the body's need for water. Dry or salty food and dry, dusty air may induce such a sensation by depleting moisture in the mucous membranes of the mouth and throat. Relief through ingestion of water is only temporary, however, if thirst results from a generalized depletion of water in the system. About three fourths of the body is composed of fluids, and the average adult requires 21/2 qt (2.4 liters) of fluid per day, supplied by water, other beverages, and foods. Depriving the body of water interferes with its metabolism and functions, causing dehydration, which is eventually fatal. The unnatural thirst that accompanies fever, diabetes, and other disorders is caused by a rapid reduction of the body fluids. The sensation of thirst is controlled by osmoreceptors in the hypothalamus in the brain. Dehydration of the cells triggers the posterior pituitary to releast the antidiuretic hormone (ADH).